Measurement setup, reference reflector as well as method for measuring attenuation

ABSTRACT

A measurement setup for measuring attenuation through an irregular surface of a device under test is described. The measurement setup comprises a positioning system, a reference reflector having a collection of diffuse scattering members, and a three dimensional imaging system. The measurement setup has a reference state and a measurement state, wherein respective images are taken in the different states. The imaging system is configured to compare the images taken in the reference state and the measurement state to determine the attenuation of the device under test. Further, a reference reflector as well as a method for measuring attenuation are described.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate generally to a measurementsetup for measuring attenuation through an irregular surface of a deviceunder test. Further, embodiments of the present disclosure relategenerally to a reference reflector for use in a measurement setup formeasuring attenuation through an irregular surface. Embodiments of thepresent disclosure also relate generally to a method for measuringattenuation of an irregular surface of a device under test.

BACKGROUND

Nowadays, radar sensors are used in vehicles for observing theenvironment of the respective vehicle, for instance the distance to apreceding vehicle or rather the distance to a vehicle behind is observedby the radar sensors. A driver of the vehicle may be warned if adistance observed becomes too small. Typically, the radar sensors aremounted behind the front car bumper as well as the rear car bumper.Since the car bumpers are painted with a metallic paint, undesirableattenuations of the radar signals occur which are caused by the paint.

Generally, the occurring attenuation is highly dependent on the paintcolor, its density, its metallic content, its thickness, its mixture andso on. Thus, it is hard to control or rather to predict the resultingattenuation value of a car bumper in industrial production since eachindividual paint has to be examined individually.

The measurement of the attenuation is further complicated as the carbumpers typically have an irregular surface.

So far, point-like measurements are done in industrial productionwherein a few singular points are investigated. The complete field ofview of the radar sensors, also called radar field of view, cannot becovered by such a measurement type in a practical time. Hence, it is notpossible to get a reliable overview of the attenuation of the whole carbumper.

For scientific or rather academic applications, a radio frequency sensormodule can be used that is remotely placed behind the respective carbumper wherein a direct transmission measurement is performed, forinstance the scattering parameter S21 obtained by a vector networkanalyzer is taken into account. However, these measurements areimpractical in industrial production due to several facts, for instancehigh tolerances and the radio frequency cables that have to be extendedinto the inside body of the bumper.

Accordingly, there is a need for a possibility to measure attenuationthrough an irregular surface of a device under test such as a car bumperin a practical and cost-efficient manner so that it can be applied inindustrial production of the respective device under test.

SUMMARY

Embodiments of the present disclosure provide a measurement setup formeasuring attenuation through an irregular surface of a device undertest, comprising:

-   -   a positioning system;    -   a reference reflector having a collection of diffuse scattering        members;    -   a three dimensional imaging system having a field of view, the        three dimensional imaging system being configured to use        electromagnetic signals in the frequency range of a radar        system;    -   the measurement setup having a reference state and a measurement        state;    -   the positioning system, in the reference state, being configured        to position the reference reflector without the device under        test in the field of view of the imaging system;    -   the positioning system, in the measurement state, being further        configured to position the reference reflector and the device        under test in the field of view of the imaging system, the        device under test being located between the imaging system and        the reference reflector;    -   the imaging system, in the reference state, being configured to        take a reference image of the reference reflector;    -   the imaging system, in the measurement state, being configured        to take a measurement image of the reference reflector while the        device under test is arranged between the imaging system and the        reference reflector;    -   the imaging system being further configured to compare the        images taken in the reference state and the measurement state to        determine the attenuation of the device under test.

Accordingly, the attenuation of the device under test having anirregular surface such as a car bumper can be measured easily and in acost-efficient manner by the measurement setup since reflection imagingagainst a reference target is used for generating a reference image. Thereference image, namely the image taken in the reference state, is laterused for comparison purposes in order to determine the attenuation ofthe device under test with its irregular surface. Put it another way,the attenuation of the device under test is obtained by measuring thecollective relative change in the reflectivity of the diffuse scatteringmembers of the reference reflector used in both measurements, namely thereference measurement as well as the measurement of the device undertest. Thus, the reflection of the device under test itself, namely itsirregular shape, is removed as this reflection occurs at a wrongreflection plane, namely a reflection plane being distanced to thereference reflector. In fact, the imaging system relies on thereflection of the reference reflector for determining the attenuation ofthe device under test.

The three dimensional imaging system uses electromagnetic signals in thefrequency range of radar systems, for instance an ultimate radar system.The applied frequency range corresponds to the one of the radar sensorsused by the device under test, for instance the car bumper. Thus, theelectromagnetic signals may have a frequency between 75 and 82 GHz, forinstance a frequency of 77 GHz or 79 GHz, so that the wavelength of theelectromagnetic signals corresponds substantially to 4 mm. Thus, thethree dimensional imaging system may be a highly resolved millimeterwave panel (mmWave panel) so as to image through the device under test,namely the reference reflector placed behind the device under test.

Generally, the three dimensional imaging system has a defined radiationpattern, namely radiation beam(s), so that the electromagnetic signalsimpinge on the device under test in a defined manner.

As the measurement setup relies on the reflection of the referencereflector, it becomes obvious that at least a part of the signalsemitted by the three dimensional imaging system goes through the deviceunder test, for example in a parallel or rather straight manner. Hence,the transmission thickness, namely the thickness of the material of thedevice under test to be traversed by the electromagnetic signals, isconstant.

In the measurement state, the reference reflector may be located insidethe device under test, namely the car bumper. Hence, the referencereflector may be embedded in the device under test. Alternatively, thereference reflector is positioned (closely) behind the device undertest, for example directly behind. In fact, the reference reflector ispositioned to correspond to the intended position of the at least oneradar sensor being used by the device under test.

The positioning system ensures that the reference reflector ispositioned in the correct position. For this purpose, the positioningsystem may position the reference reflector in the reference state andin the measurement state so that the same location of the referencereflector is ensured for the reference reflector during bothmeasurements, namely the reference measurement and the measurement ofthe device under test.

The collection of the diffuse scattering members may correspond to amatrix so that the individual scattering members are located in amatrix-like arrangement. The respective distances between neighboredscattering members may be equal. Thus, the individual scattering memberscan be distributed over a surface of the reference reflector in ahomogeneous manner.

The diffuse scattering members ensure that the electromagnetic signalsradiated by the three dimensional imaging system are scattered in alldirections.

According to an aspect, the imaging system is configured to locate thereference reflector and its scattering members by using geometricmatching. This can be ensured due to the reference image taken in thereference state since only the reference reflector is located in thefield of view of the three dimensional imaging system. Thus, therespective locations of the individual scattering members can be locatedby the imaging system. The imaging system can locate and extract thecollective reflectivity of the reference reflector at the individualscattering members. Put it another way, the three dimensional imagingsystem, in the measurement state, already knows the locations of thediffuse scattering members or at least expects the individual scatteringmembers at certain locations (due to the same position of the referencereflector and the geometric matching). Accordingly, the referenced imagetaken provides some kind of a template with regard to the locations ofthe individual scattering members. By using this template in themeasurement state, the imaging system is enabled to identify thescattering members in the image taken in the measurement state moreeasily.

For instance, locations within a range of 3 mm deviation of thetemplate, namely 3 mm to the left and/or 3 mm to the right of theexpected locations, may be taken into account. Hence, minor deviationsdo not impair the measurement result.

Another aspect provides that the imaging system being configured tocompare the image strength at the locations of at least two scatteringmembers of the reflector while comparing the images taken in thereference state and the measurement state. The attenuation of the deviceunder test can be retrieved easily by taken the image strength intoaccount of both images taken so that the attenuation merely correspondsto the difference in reflectivity strength of both images. Since thereflectivity strength or rather the image strength is taken into accountat the location of scattering members, it becomes obvious that theirregular surface of the device under test is not taken into account. Infact, reflections at the irregular surface are assigned to a differentreflection plane compared to the one of the reference reflector. Inother words, the reflection of the device under test itself, namely itsirregular surface, is removed so that these signals do not contribute tothe determination of the attenuation of the device under test.

According to an aspect, the imaging system is further configured todisregard the reflection originating from the irregular surface. Theimaging system only relies on reflections of the reference reflector fordetermining the attenuation of the device under test. Since theirregular surface is assigned to a different reflection plane, thesereflections do not contribute. In fact, disturbing contributions of theirregular surface are disregarded since the imaging system relates tothe reflection plane assigned to the reference reflector.

Moreover, the imaging system may be configured to take only thescattering members into account that contribute to the intersectionbetween the irregular surface of the device under test and an intendedfield of view of at least one radar sensor of the device under test. Theintended field of view of the at least one radar sensor, also calledradar field of view, corresponds to a specific area on the irregularsurface of the device under test. As this area is of interest for theattenuation determination, only these scattering members are taken intoaccount that have a contribution to this specific area. The other areasof the irregular surface which do not intersect with the radar field ofview are less interesting so that the scattering members assigned tothese areas are neglected. Put it another way, some scattering membersare excluded if they are located outside of the intended radar field ofview of the device under test on the irregular surface of the deviceunder test. Thus, only specific scattering members are selected that arerelevant for the intended radar field of view with respect to theirregular surface of the device under test.

Moreover, the reference reflector may be positioned by the positioningsystem such that the scattering members face the imaging system. Hence,the electromagnetic signals transmitted by the imaging system impinge onthe scattering members of the reference reflector (after traversing thedevice under test in the measurement state) so that the electromagneticsignals are reflected by the scattering members. In fact, the scatteringmembers reflect the electromagnetic signals towards the imaging system.

The imaging system is generally configured to receive the reflectedelectromagnetic signals and to process these signals appropriately.

The field of view of the imaging system may be aligned with a radarfield of view provided by at least one radar sensor of the device undertest. The electromagnetic signals emitted by the imaging system maycross the irregular surface of the device under test in the same area asthe radar signals of the intended radar field of view do. Thus, thewhole intersection surface, namely the surface area of the irregularsurface that is intersected by the radar field of view, is radiated bythe three dimensional imaging system. In addition, neighbored areas onthe irregular surface are not irradiated by the imaging system.

Moreover, the positioning system may be at least one of a fixedpositioning system and a movable positioning system. The fixedpositioning system ensures that at least the reference reflector is heldat the same position during both measurement. The moveable positioningsystem is enabled to irradiate the device under test under differentpositions with regard to the imaging system. However, the moveablepositioning system also ensures that the reference reflector is held inthe same position during the reference measurement as well as themeasurement of the device under test as it the positioning system iscontrolled to take the same position.

For instance, the positioning system comprises a robot. The robot can becontrolled appropriately so that the desired positions for the referencereflector as well as the device under test can be obtained.

Another aspect provides that the positioning system comprises at leastone gripper being configured to position at least one of the referencereflector and the device under test. The gripper can be used for easilyholding the at least one respective component, namely the referencereflector and/or the device under test.

In some embodiments, the gripper is capable of holding the irregularsurface of the device under test in the desired position, namely infront of the reference reflector.

For instance, the at least one gripper has a vacuum sucker. The deviceunder test with its irregular surface can be held easily by the gripper.Further, the component may be gripped at different locations easilywithout any wear.

The positioning system may be free of highly reflective components inthe area used for measuring the attenuation. The measurements are notdisturbed by reflections of the positioning system.

For instance, at least the gripper is free of highly reflectivecomponents since the gripper is located close to the reference reflectorand/or the device under test during the respective measurement.

The reference reflector may comprise a base to which the severalindividual scattering members are attached. The several individualscattering members each may have a curved tip for reflection. The sizeof the several individual scattering members in some embodiments iscomparable to the wavelength of a signal used for attenuationmeasurement, the several individual scattering members being arrangedwith regard to the base such that front and back reflections occur whichare separable by the imaging system. Thus, the distance between the tipsof the individual scattering members and the base to which the severalindividual scattering members are attached by their opposite ends ishigh enough so that the imaging system can separate the reflections thatoccur at the base and the tips of the several individual scatteringmembers. Thus, two reflection planes are provided by the referencereflector.

In some embodiments, the base comprises an electromagnetic absorber. Theelectromagnetic absorber ensures that background reflection is reduced,namely the back reflection. The absorber may be provided by anelectromagnetic absorbing layer. The layer may be painted, sprayedand/or coated on the base.

In some embodiments, the curved tip may be ellipsoidal or hemisphere.

In some embodiments, the scattering members may be formed by stickshaving a diameter corresponding to the wavelength of the signal used formeasurement. Thus, the individual scattering members are shapedsubstantially cylindrical with a certain diameter.

Further, embodiments of the present disclosure provide a referencereflector for use in a measurement setup for measuring attenuationthrough an irregular surface. The reference reflector comprises a baseand several individual scattering members attached to the base. Theseveral individual scattering members in some embodiments each have acurved tip for reflection, and the size of the several individualscattering members being comparable to the wavelength of a signal usedfor attenuation measurement. The several individual scattering membersare arranged with regard to the base such that front and backreflections occur which are separable by an imaging system. The frontreflection may occur by the tips of the several individual scatteringmembers whereas the back reflection is assigned to the reflection at thebase. Thus, the several individual scattering members are long enough sothat the imaging system can differentiate between both reflectionplanes.

The base may comprise an electromagnetic absorber. The electromagneticabsorber ensures that background reflection is reduced, namely the backreflection. The absorber may be provided by an electromagnetic absorbinglayer. The layer can be provided by a paint, a spray and/or coating.

Further, embodiments of the present disclosure provide a method formeasuring attenuation of an irregular surface of a device under test,with the following steps:

-   -   positioning a reference reflector having a collection of diffuse        scattering members in front of a three dimensional imaging        system that uses electromagnetic signals in the frequency range        of a radar system;    -   taking a reference image of the reference reflector by using the        imaging system;    -   positioning the device under test and the reference reflector in        front of the imaging system so that the device under test is        arranged between the reference reflector and the imaging system;    -   taking a measurement image of the reference reflector while the        device under test is arranged between the imaging system and the        reference reflector by using the imaging system; and    -   comparing the images taken to determine the attenuation of the        device under test.

The characteristics and advantages mentioned above with regard to themeasurement setup also apply for the method mentioned above in a similarmanner.

In some embodiments, the collective reflectivity at the scatteringmembers is located and extracted by the imaging system after thereference image was taken. In a similar manner, the collectivereflectivity at the scattering members is located and extracted by theimaging system after the measurement image was taken. Hence, therespective collective reflectivity can be compared.

When comparing both images, the attenuation can be determined easilywhile referring to the collective reflectivity at the scatteringmembers, for example the difference.

According to an aspect, the image strength at the locations of at leasttwo scattering members of the reference reflector are compared whilecomparing the images taken. The attenuation of the device under test isdetermined by comparing the image strength of the reflected signal atlocations assigned to the reference reflector. Hence, the referenceplane assigned to the reference reflector is taken into account. Inother words, the reflection of the irregular surface of the device undertest is removed as it is assigned to a different reflection plane.

According to another aspect, reflection originating from the irregularsurface is disregarded. Thus, only the reflections occurring fromscattering members of the reference reflector, for example the onesassigned to the radar field of view, are taken into account formeasurement purposes. In some embodiments, the reflections originatingfrom the irregular surface are assigned to a different reflection planecompared to the one of the reference reflector.

Moreover, only the scattering members in some embodiments are taken intoaccount that contribute to the intersection between the irregularsurface of the device under test and an intended field of view of atleast one radar sensor of the device under test. Thus, a certain area ofthe irregular surface of the device under test is measured with regardto attenuation since this area will be irradiated by the intended radarfield of view of the at least one radar sensor of the device under test.In fact, only this area of the irregular surface is of interest withregard to the transmittance of the device under test.

The attenuation of the device under test can be determined by averagingattenuation values due to the attenuation values determined for therespective scattering members taken into account.

DESCRIPTION OF THE DRAWINGS

The foregoing aspects and many of the attendant advantages of theclaimed subject matter will become more readily appreciated as the samebecome better understood by reference to the following detaileddescription, when taken in conjunction with the accompanying drawings,wherein:

FIG. 1 shows a measurement setup in a reference state according to thepresent disclosure;

FIG. 2 shows the measurement setup of FIG. 1 in a measurement state;

FIG. 3 shows the measurement setup of FIG. 2 in another perspective viewwithout positioning system;

FIG. 4 shows a detail of FIG. 3;

FIG. 5 shows a perspective view of a reference reflector according tothe present disclosure;

FIG. 6 shows a top view of the reference reflector of FIG. 5;

FIG. 7 shows a side view of the reference reflector of FIGS. 5 and 6;and

FIG. 8 shows a flow-chart illustrating a method for measuringattenuation according to the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings, where like numerals reference like elements, is intended as adescription of various embodiments of the disclosed subject matter andis not intended to represent the only embodiments. Each embodimentdescribed in this disclosure is provided merely as an example orillustration and should not be construed as preferred or advantageousover other embodiments. The illustrative examples provided herein arenot intended to be exhaustive or to limit the claimed subject matter tothe precise forms disclosed.

In FIG. 1, a measurement setup 10 for measuring attenuation through anirregular surface of a device under test is shown in a reference state.As shown in FIG. 1, the measurement setup 10 comprises a threedimensional system 12 that has several antennas for transmitting and/orreceiving electromagnetic signals as will be described later. The threedimensional imaging system 12 uses electromagnetic signals in thefrequency range of a radar system such as an ultimate radar system.Thus, the electromagnetic signals may have a frequency between 75 and 82GHz, for example 77 GHz and 79 GHz, so that the wavelength of theelectromagnetic signals corresponds to 4 mm. Therefore, the threedimensional imaging system 12 is also called mmWave imaging system.

The measurement setup 10 further comprises a positioning system 14 thathas a robot 16 and at least one gripper 18 for gripping components andholding the respective component in a desired position. The at least onegripper 18 may be located at an end of a robotic arm of the robot 16. Inthe shown embodiment, the gripper 18 has a vacuum sucker 20 so that therespective component is held by the gripper 18 via a vacuum applied.

In FIG. 1, the measurement setup 10 is shown in its reference statewherein the measurement setup 10 is used to take a reference image of areference reflector 22 that is held by the at least one gripper 18 in areference position. The reference reflector 22 is shown in more detailin FIGS. 5 to 7. The reference reflector 22 comprises a base 24 beingprovided by a plate from which diffuse scattering members 26 extend in asubstantially perpendicular direction.

As shown in FIGS. 5-7, the diffuse scattering members 26 are arranged ina matrix on the base 24 wherein the scattering members 26 each have acurved tip 28, for instance a hemisphere or an ellipsoidal tip, so thatelectromagnetic signals impinging on the scattering members 26 arescattered in a diffuse manner. The size of the several individualscattering members 26 is substantially comparable to the wavelength ofthe signals emitted by the imaging system 12. Particularly, thescattering members 26 are shaped cylindrically wherein their diametercorresponds to the wavelength of the electromagnetic signals emitted bythe imaging system 12, namely about 4 mm.

Furthermore, the several individual scattering members 26 have a lengththat ensures that two different reflection planes are provided by thereference reflector 22 which can be differentiated by the imaging system12. The reflection planes provided correspond to the reflection at thetips 28, also called front reflection, as well as reflections at thebase 24, also called back reflection. Hence, front and back reflectionsoccur when the electromagnetic signal impinges on the referencereflector 22. In some embodiments, the scattering members 26 correspondto sticks.

As shown in FIG. 6, the individual scattering members 26 are spacedapart from each other by substantially the same distance so that ahomogenous distribution of scattering members 26 is obtained.

Returning to FIG. 1, the field of view 30 of the imaging system 12 isillustrated appropriately which irradiates the reference reflector 22via a certain area as will be described later with respect to FIG. 2.

For measuring the attenuation of a device under test, the referencereflector 22 is positioned in front of the imaging system 12 via thepositioning system 14 in a first step S1 (see FIG. 8). The referencereflector 22 is positioned such that the scattering members 26 face theimaging system 12 so that the electromagnetic signals emitted by theimaging system 12 impinge on the scattering members 26 which scatter thesignals in a diffuse manner.

In a second step S2, the imaging system 12 takes a reference image ofthe reflectance of the reference reflector 22. Particularly, the imagestrength at the different locations assigned to the scattering members26 is evaluated by the imaging system 12. Hence, the collectivereflectivity at the individual scattering members 26 is located andextracted so that a template with regard to the locations of theindividual scattering members 26 is obtained.

In a next step S3, which is illustrated in FIG. 2, a device under test32 is held by the positioning system 14 wherein the device under test 32is positioned between the imaging system 12 and the reference reflector22.

Then, the device under test 32 as well as the reference reflector 22positioned behind the device under test 32 are irradiated by the imagingsystem 12 (step S4). Thus, the electromagnetic signals emitted by theimaging system 12 go through the device under test 32 and impinge on thereference reflector 22 located being the device under test 32. Theelectromagnetic signals are attenuated by the device under test 32 whilethey go through (transverse) the device under test 32. Again, theimaging system 12 locates and extracts the collective reflectivity atthe individual scattering members 26 so that a measurement image of thereference reflector 22 is taken while the device under test 32 isdisposed between the imaging system 12 and the reference reflector 22.

After the imaging system 12 has taken the reference image (S2) as wellas the measurement image (S4), the imaging system 12 compares the imagestaken so as to determine the attenuation of the device under test 32(step S5).

Therefore, the imaging system 12 relies on a geometric matching withregard to the reference reflector 22 which can be done since the imagingsystem 12 has taken the reference image in advance so that the differentscattering members 26.

The positioning system 14 generally ensures that the reference reflector22 is positioned in the same position for both the reference measurementand the measurement of the device under test 32. Hence, a relativereflection imaging against the reference reflector 22 is used fordetermining the attenuation of the device under test 32. In other words,the geometric matching is done by the imaging system 12 so as to locatethe reference reflector 22, for example its scattering members 26, inthe measurement state compared to the reference state. Therefore, thethree dimensional imaging system 12, in the measurement state, alreadyknows the locations of the diffuse scattering members 26 due to thegeometric matching or at least expects the individual scattering members26 at certain locations

As already discussed, the device under test 32 may be a car bumpercomprising a radar sensor with an intended radar field of view 34 asillustrated in FIG. 2. The field of view 30 of the imaging system 12corresponds to the intended radar field of view 34 as will becomeobvious by taking FIGS. 3 and 4 into account. In other words, the fieldof view 30 of the imaging system 12 is aligned with the radar field ofview 34.

Thus, the attenuation of the irregular surface of the device under test32 can be determined for the specific area that interacts with the atleast one radar sensor of the device under test 32 in real application.The attenuation is measured for the intersection of the radar field ofview 34 and the irregular surface of the device under test 32 since thefield of view 30 of the imaging system 12 covers the same area at theirregular surface of the device under test 32.

The imaging system 12 is further configured in some embodiments to takeonly the scattering members 26 into account that contribute to theintersection between the irregular surface of the device under test 32and the radar field of view 34 of the at least one radar sensor of thedevice under test 32 or rather the field of view 30 of the imagingsystem 12 covering the same area on the irregular surface. Thus, thecontributions of the scattering members 26 are only used for determiningthe attenuation of the device under test 32 that may have an influenceon the signal attenuation in real operation.

As already discussed above, the imaging system 12 relies on thereflections that occur on the reference reflector 22 for determining theattenuation of the device under test 32. The scattering members 26 ofthe reference reflector 22 itself are long enough so that two differentreflection planes occur, namely the one assigned to the tips 28 of thediffuse scattering members 26 and the one assigned to the base 24. Insome embodiments, the base 24 may be covered by an electromagneticabsorber 36 so that background reflection is reduced, namely the backreflection at the base 24. The electromagnetic absorber 36 may beprovided by a layer that can be established by a spray, a coating and/ora paint. Therefore, the imaging system 12 substantially receives onlythe reflections that occur at the tips 28 of the scattering members 26.

The imaging system 12 is also configured to disregard reflections fromthe irregular surface as these reflections are also assigned to adifferent reflection plane with respect to the reflection plane of thereference reflector 22, for example the reflection plane of the tips 28.

For improving the measurements, the positioning system 14 is free ofhighly reflective components in the area used for measuring theattenuation of the device under test 32. This can already be ensured byproviding the gripper 18 without any highly reflective components sincethe gripper 18 is assigned to the measurement area where the referencereflector 22 and/or the device under test 32 are/is held by the gripper18 during the respective measurement.

Generally, the positioning system 14 may be a fixed positioning systemso that the location of the reference reflector 22 is always the same.Alternatively, the positioning system 14 may be a moveable positioningsystem wherein the positioning system 14 is controlled appropriately sothat it can be ensured that the reference reflector 22 is positioned orrather moved in the same position for measurement. The movablepositioning system 14 generally ensures that differently sized devicesunder test 32 can be tested easily by the measurement setup 10.

In general, the imaging system 12 is enabled to take only a certainreflection plane into account for determining the attenuation. Thereflection plane used is assigned to the tips 28 of the diffusescattering members 26.

In fact, reflections being too close, namely those of the irregularsurface of the device under test 32, are not taken into considerationfor determining the attenuation of the device under test 32. In asimilar manner, reflections at the base 24 of the reference reflector 22are disregarded by the imaging system 12. Those reflections are alreadysuppressed by the electromagnetic absorber 36.

Hence, each diffuse scattering member 26 scatters the respectiveelectromagnetic signals towards the imaging system 12 that in turn canneglect certain scattering members 26, for example their reflectedsignals, so that only those reflections are taken into account thatcorrespond to the intersection of the radar field of view 34 and theirregular surface of the device under test 32.

Using the reference reflector 22 ensures that the attenuation of thedevice under test 32 having an irregular surface can be done easily andin a cost-efficient manner. Accordingly, the respective measurements canbe done at industrial sites so that the radar systems of a vehicle canbe calibrated more easily.

The principles, representative embodiments, and modes of operation ofthe present disclosure have been described in the foregoing description.However, aspects of the present disclosure which are intended to beprotected are not to be construed as limited to the particularembodiments disclosed. Further, the embodiments described herein are tobe regarded as illustrative rather than restrictive. It will beappreciated that variations and changes may be made by others, andequivalents employed, without departing from the spirit of the presentdisclosure. Accordingly, it is expressly intended that all suchvariations, changes, and equivalents fall within the spirit and scope ofthe present disclosure, as claimed.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A measurement setup formeasuring attenuation through an irregular surface of a device undertest, comprising: a positioning system; a reference reflector having acollection of diffuse scattering members; a three dimensional imagingsystem having a field of view, the three dimensional imaging systembeing configured to use electromagnetic signals in the frequency rangeof a radar system; the measurement setup having a reference state and ameasurement state; the positioning system, in the reference state, beingconfigured to position the reference reflector without the device undertest in the field of view of the imaging system; the positioning system,in the measurement state, being further configured to position thereference reflector and the device under test in the field of view ofthe imaging system, the device under test being located between theimaging system and the reference reflector; the imaging system, in thereference state, being configured to take a reference image of thereference reflector; the imaging system, in the measurement state, beingconfigured to take a measurement image of the reference reflector whilethe device under test is arranged between the imaging system and thereference reflector; the imaging system being further configured tocompare the images taken in the reference state and the measurementstate to determine the attenuation of the device under test.
 2. Themeasurement setup according to claim 1, wherein the imaging system isconfigured to locate the reference reflector and its scattering membersby using geometric matching.
 3. The measurement setup according to claim1, wherein the imaging system is configured to compare the imagestrength at the locations of at least two scattering members of thereference reflector while comparing the images taken in the referencestate and the measurement state.
 4. The measurement setup according toclaim 1, wherein the imaging system is further configured to disregardthe reflection originating from the irregular surface.
 5. Themeasurement setup according to claim 1, wherein the imaging system isconfigured to take only the scattering members into account thatcontribute to the intersection between the irregular surface of thedevice under test and an intended field of view of at least one radarsensor of the device under test.
 6. The measurement setup according toclaim 1, wherein the reference reflector is positioned by thepositioning system such that the scattering members face the imagingsystem.
 7. The measurement setup according to claim 1, wherein the fieldof view of the imaging system is aligned with a radar field of viewprovided by at least one radar sensor of the device under test.
 8. Themeasurement setup according to claim 1, wherein the positioning systemis at least one of a fixed positioning system and a movable positioningsystem.
 9. The measurement setup according to claim 1, wherein thepositioning system comprises a robot.
 10. The measurement setupaccording to claim 1, wherein the positioning system comprises at leastone gripper being configured to position at least one of the referencereflector and the device under test.
 11. The measurement setup accordingto claim 10, wherein the at least one gripper has a vacuum sucker. 12.The measurement setup according to claim 1, wherein the positioningsystem is free of highly reflective components in the area used formeasuring the attenuation.
 13. The measurement setup according to claim1, wherein the reference reflector comprises a base to which the severalindividual scattering members are attached, the several individualscattering members each having a curved tip for reflection, the size ofthe several individual scattering members being comparable to thewavelength of a signal used for attenuation measurement, the severalindividual scattering members being arranged with regard to the basesuch that front and back reflections occur which are separable by theimaging system.
 14. The measurement setup according to claim 1, whereinthe scattering members are formed by sticks having a diametercorresponding to the wavelength of the signal used for attenuationmeasurement.
 15. A method for measuring attenuation of an irregularsurface of a device under test, with the following steps: positioning areference reflector having a collection of diffuse scattering members infront of a three dimensional imaging system that uses electromagneticsignals in the frequency range of a radar system; taking a referenceimage of the reference reflector by using the imaging system;positioning the device under test and the reference reflector in frontof the imaging system so that the device under test is arranged betweenthe reference reflector and the imaging system; taking a measurementimage of the reference reflector while the device under test is arrangedbetween the imaging system and the reference reflector by using theimaging system; and comparing the images taken to determine theattenuation of the device under test.
 16. The method according to claim15, wherein the image strength at the locations of at least twoscattering members of the reference reflector are compared whilecomparing the images taken.
 17. The method according to claim 15,wherein reflection originating from the irregular surface isdisregarded.
 18. The method according to claim 15, wherein only thescattering members are taken into account that contribute to theintersection between the irregular surface of the device under test andan intended field of view of at least one radar sensor of the deviceunder test.